With the wider band of a radio communication, multicarrier communication systems that divide Tx information into a plurality of frequency bands (hereinafter referred to as “subcarriers”) to conduct a communication are used. Among the multicarrier communication systems, an orthogonal frequency division multiplexing (OFDM) system narrows the bandwidth of each subcarrier to improve a resistance to a delay wave, and uses the orthogonality of a signal to render a guard band between the subcarriers unnecessary, thereby enabling a high-frequency use efficiency to be realized. Therefore, the OFDM system is applied in a wide range of systems such as worldwide interoperability of microwave access (WiMAX) or long term evolution (LTE).
In each radio device of those systems, particularly in a base station device that conducts a communication with a large number of terminal devices, it is desirable to aggregate signal processing in the neighborhood of an antenna in order to prevent attenuation of a signal within the base station device. On the other hand, the scale of the device that can be arranged in the neighborhood of the antenna is limited, and according to a requirement of dealing with a communication technology using a plurality of antennas located at distances from each other, there is used a radio device having a remote radio unit arranged in the neighborhood of each antenna, and a baseband unit additionally arranged, in which those units are connected by a digital signal.
Because the radio device having the above configuration is normally used, for example, in CPRI Specification V4.0, Common Public Radio Interface (CPRI); Interface Specification, issued on Jun. 30, 2008, an interface between the baseband unit called “radio equipment control” and the remote radio unit called “radio equipment” is defined as standard.
Also, apart from the interface disclosed in CPRI Specification V4.0, Common Public Radio Interface (CPRI); Interface Specification, issued on Jun. 30, 2008, for example, JP-A-2007-274048 discloses a technique in which the baseband unit called “baseband processor” and the remote radio unit called “radio unit” are interfaced in a frequency domain.